Rename files to preserve history

Test\Eslint fail - this is expected.

Change-Id: I7f4d1cfaa65651870f645fcf28b1e66ebe3d1895
diff --git a/polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences.js b/polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences.ts
similarity index 100%
rename from polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences.js
rename to polygerrit-ui/app/elements/shared/gr-diff-preferences/gr-diff-preferences.ts